Thacher calculating machine, 1880s. The Thacher calculating instrument was patented in 1881. It was cylindrical and could slide back and forth, giving it the power of several individual slide rules. It could do multiplication and division, and calculate interest, roots and powers of numbers to about five significant figures. It was also accurate to within about 0.01 percent, which was incredible accuracy for that time. It was designed by US bridge engineer Edwin Thacher (1839-1920), and marketed by the Keuffel and Esser instrument-making company.